A number of chemicals and consumer products may be produced utilizing fermentation as the manufacturing process. For example, alcohols such as ethanol and butanol have a variety of industrial and scientific applications such as fuels, reagents, and solvents. Butanol is an important industrial chemical useful as a fuel additive, as a feedstock chemical in the plastics industry, and as a food grade extractant in the food and flavor industry. Each year 10 to 12 billion pounds of butanol are produced by chemical syntheses using starting materials derived from petrochemicals. The production of butanol or butanol isomers from materials such as plant-derived materials could minimize the use of petrochemicals and would represent an advance in the art. Furthermore, production of chemicals and fuels using plant-derived materials or other biomass sources would provide eco-friendly and sustainable alternatives to petrochemical processes.
Techniques such as genetic engineering and metabolic engineering may be utilized to modify a microorganism to produce a certain product from plant-derived materials or other sources of biomass. The microorganism may be modified, for example, by the insertion of genes such as the insertion of genes encoding a biosynthetic pathway, deletion of genes, or modifications to regulatory elements such as promoters. A microorganism may also be engineered to improve cell productivity and yield, to eliminate by-products of biosynthetic pathways, and/or for strain improvement. Examples of microorganisms expressing engineered biosynthetic pathways for producing butanol isomers, including isobutanol, are described in U.S. Pat. Nos. 7,851,188 and 7,993,889.
However, exposure to alcohols such as ethanol and butanol during fermentation can have a negative impact on cell viability, cell productivity, and product yield. The accumulation of these alcohols can inhibit cell growth and eventually affect the fermentative production of these alcohols. As such, there is a need to develop microorganisms that exhibit improved cell growth and production in the presence of these alcohols as well as methods that maintain and/or improve cell viability and cell productivity.
The present invention is directed to the development of such methods as well as the development of microorganisms with improved cell viability and cell productivity and capable of producing fermentation products via an engineered pathway in the microorganisms.